Specifications
Page A-3SCSI Termination
2.For AM-2001 subsystem installations, the last SCSI device attached to the
connector farthest down the cable away from the host computer must have its
terminators installed. All SCSI devices inside the host computer must have their
terminators removed. If you are mixing SCSI-1 and SCSI-2 disk drives, do not
terminate the last SCSI device in the subsystem; instead, plug an external
terminator (PRA-00222-00) into the open rear panel SCSI connector on the rear
panel of the AM-2001 subsystem. This will properly terminate all SCSI-1 and
SCS-2 devices in both the host computer and the subsystem.
A.2TERMINATION POWER
In order to properly control SCSI bus termination, a termination power source must be
provided; this is especially important when using an external terminator.
Why is Termination Power so important when using an external terminator?
In order for terminators to do their job, they must have a power source. In most (but not
all) cases, a SCSI peripheral will supply termination power to its own on-board
terminators, even if the SCSI host controller or no other SCSI peripheral is supplying
termination power to the SCSI bus. However, for an external terminator to be effective
there has to be termination power supplied to the SCSI bus. If no termination power is
available, the external terminator is not going to do its job, which means your SCSI bus
is not terminated. This may result in a computer that either won’t boot or once booted
may tend to hang frequently. Because SCSI-2 devices transfer data at a higher rate,
they are more prone to display problems when improperly terminated.
The termination power source can be configured in one of two ways, depending on your
application:
AMOS based computers with SCSI-2 implementation (i.e., AM-4000 computers,
AM-540 enhanced AM-3000M computers, all Roadrunner enhanced computers,
etc) should be configured to supply termination power via the host controller.
When termination power is supplied by the host controller, it is not necessary to
have one of your internally mounted SCSI peripherals configured to supply
termination power to the SCSI bus.
AMOS computers using the 50-pin SASI bus, which includes non-SCSI-2
enhanced AM-1000, AM-1200, AM-1400, AM-1600, AM-2000, AM-2000M,
AM-3000, and AM-3000M computers, require that one of the internally mounted
peripherals be configured to supply termination power to the SCSI bus.
SCSI-2 Bus Termination Power Guidelines
Use these guidelines for supplying termination power to AM-4000 computers,
Roadrunner enhanced computers, AM-540 enhanced AM-3000M computers, etc:
1.AMOS based computers with SCSI-2 implementation will be configured with the
host controller supplying termination power to the SCSI bus.
PDI-00172-40, Rev. A05